US20160109002A1 describes such a continuously variable transmission which is considered to be the closest prior art.
WO2014179717 also describes a continuously variable transmission, having a NuVinci variator, a plus planetary gear set, a minus planetary gear set, and an arrangement of multiple clutches, which makes two forward modes and one reverse mode available.
DE102013223243 describes a power-split continuously variable transmission device having a summarizing planetary transmission, at least one further planetary gear set, and a variator, which are operatively connected to each other in the area of shafts and which are coupleable to each other in the area of further shafts via shift elements in order to implement at least three ranges of ratios. A ratio is continuously variable within the ranges of ratios via the variator. The variator is a mechanical toroidal variator including at least three shafts. The summarizing planetary transmission, the at least one further planetary gear set, and the variator are arranged coaxially to each other. In one of the ranges of ratios, the total power is guidable between a transmission input shaft and a transmission output shaft via the variator. In addition, one friction wheel of the variator is at least approximately tapered at least in some areas.
Continuously variable transmissions, which are also referred to as CVT transmissions, can continuously control the transmission ratio between the lowest and the highest ratios, for example, with the aid of a so-called variator. This is different from typical transmissions, in which a number of predetermined (discrete) transmission ratios are provided. A CVT transmission can be a mechanical continuously variable transmission, for example, in the form of a flexible traction drive mechanism or a friction drive such as a cone ring or toroidal transmission.
The basic active principles of mechanical continuously variable transmissions are always the same, regardless of their construction. The power transmission takes place, without conversion of the form of energy, in a force-locking manner, by way of the friction-locking contact of two or more contact bodies which are moving relative to each other and which are usually referred to as a primary and a secondary disk, which are also referred to as a primary and a secondary side, wherein the two disks are formed from conical disks arranged in pairs and are provided with a torque-transmitting wrap-around element which revolves between the two pairs of conical disks.
Depending on the type of construction, very high full-load efficiencies are possible, which substantially exceed those of the hydrostatic transmission. The transmission ratio of mechanical CVTs is always determined by their active friction radii ratio, i.e., the current ratio is defined by the running radius of the wrap-around element, which, in turn, is a function of the axial position of the conical disks and, therefore, is subjected to geometric limits which prevent an immediate implementation of the starting process.
In order to overcome these limitations on the overall gear ratio of mechanical CVTs, it is useful to operate the mechanical CVTs in power-splitting transmission structures, such as in a combination of one or multiple planetary transmissions comprising a continuously variable transmission. Such a transmission, which is also referred to as an IVT transmission (infinitely variable transmission), can gear down between a fixed ratio value and any reduced speed in one transmission direction, i.e., infinitely, or even in the opposite direction, i.e., negatively, and so the input shaft rotates while the output shaft is at a standstill.
In the case of such a transmission, therefore, the spread of gear ratios of the variator are expandable, by reactive power-based operation at low speeds, in such a way that an immediate implementation of the starting process becomes possible, i.e., the vehicle is at a standstill with an “infinite” ratio, while the engine is running, without an additional separating clutch.
Due to the utilization as a power-split transmission, the power flow is guidable along one or multiple power paths. For example, the power is guidable along a first path by the variator or along a second path by way of the planetary transmission. The power is also returnable into the variator, whereby the load on the variator is increased during the operation of the continuously variable transmission.
The problem addressed by the present invention is that of making an alternative continuously variable transmission available, which has a simple configuration and a compact design.